Collection optics for led array with offset hemispherical or faceted surfaces

ABSTRACT

An array of LEDs ( 30 ) is provided having a lens array ( 34 ) for collecting divergent light from each LED ( 30 ). Each lens ( 34 ) in the array is associated with a respective LED ( 30 ) and has a compound shape including a curved surface ( 40 ) that may be spherical or may have an offset aspherical shape. The curved surfaces ( 40 ) are centered about each side of its associated LED ( 30 ). The lens ( 34 ) may alternatively include faceted surfaces ( 46 ) that approximate the curved lens surface.

This invention claims the benefit of U.S. Provisional Application No.60/516,382, entitled “Collection Optics for Led Array with OffsetHemispherical or Faceted Surfaces”, filed Oct. 31, 2003, the entiredisclosure of which is hereby incorporated by reference as if set forthin its entirety for all purposes.

BACKGROUND OF THE INVENTION

Solid state lighting devices such as, for example, light emitting diodes(LEDs) are used for a number of applications. One type of such solidstate lighting device is disclosed in International Patent ApplicationNo. PCT/US03/14625, filed May 28, 2003, entitled High EfficiencySolid-State Light Source And Methods Of Use And Manufacture, the detailsof which are hereby incorporated by reference.

Arrays of light-emitting diodes (LEDs) are used for many purposes. Forexample, arrays of LEDs are sometimes used in conjunction with arrays oflenses. The lens arrays are used to collect and collimate the light fromthe array of LEDs. However, since the light from LEDs emits into a widerange of angles, there is often a need to collect the light and projectit more usefully. For example, as seen in FIG. 1, an array 10 of suchlight sources 12, such as, for example, LEDs are sometimes used with anarray of lenses 14. Such lens arrays 14 are typically mounted above theLED array 10 and are used to collect and collimate the light from theLED array 10. The simplest and most common lens shape has a sphericalsurface to it, as shown in FIG. 1. The problem with the configuration inFIG. 1 is that the spherical design of each lens 16 assumes that the LED12 is a point source of light. However, in reality LEDs are not pointsources of light. Rather, LEDs project distributed light in a wide rangeof angles.

FIG. 2 shows a more accurate depiction of light emitted from an LEDarray 18. FIG. 2 shows that LEDs 20 often emit light from their sides,in which case the light is distributed and each LED 20 actually looksmore like two closely spaced sources of light, rather than a singlepoint source. Therefore, for some types of light sources, a singlespherical lens 22 is an inadequate optic because it does not adequatelygather or collect the disparate light so that it is more usefullyprojected. This makes the simple plano-convex lens an inappropriateshape for efficiently collecting and directing the light from such LEDsources. In order to adequately collect such disparate light, two ormore lenses would be required for each light source or LED.

In order to overcome the above-described problems, some light sourcesinclude a focusing optic that has an aspherical surface to collectdisparate light from a source. The configuration of the asphericalsurface for any given application may be determined, for example, byusing typical lens makers equations know to those skilled in the art.Thus, the optimal aspheric shape for a collimating optic used with ahighly divergent source such as an LED may be calculated. Asphericalsurfaces are a well-established means of collimating the light fromhighly divergent sources. However, aspherical optics are complex andoften too expensive and/or require expensive tooling to be practical.Even spherical lens arrays can be too expensive to manufacture for somelow-cost, high-volume applications.

Examples of these various means of collimating the light from and LEDare found in the following U.S. patents to Marshall et al (U.S. Pat. No.6,547,423), Wu (U.S. Pat. No. 6,502,956), and Suzuki (U.S. Pat. No.6,330,017), the details of which are herein incorporated by reference.

What is needed is a low-cost optic for a highly distributed anddivergent light source that collects the light so that it is projectedin a concentrated beam.

Additionally, what is needed is a low-cost solution for approximatingcomplex optical surfaces to give adequate collection efficiency forarrays of light sources for lighting (non-imaging) applications.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a lens array for use with anarray of LEDs is provided in which each lens has a compound shape, butis still constructed of curved surfaces. Since each side of the LEDemits primarily into the curved hemisphere on that side, each side ofthe LED emits light that primarily transmits through what looks like aplano-convex lens centered over that side. This means that the geometryof the curved surfaces is optimized for each portion of the LED fromwhich it collects light. Therefore, only one lens may be used for eachlight source or LED.

Another aspect of this invention uses cut facets to approximate theshape of either a spherical or an aspheric surface. These facets may bemachined into a tool that works like a drill bit, or they may bemachined by a router or grinder. When used in conjunction with a customdrill bit, the faceted angles will lie on a circularly symmetricsurface. When used in conjunction with a router or grinder, the facetscan be used to build tiered structures, such as micro-pyramids, in, forexample, a square tile pattern that fully fills the surface. The facetedapproach can accommodate flattened shapes necessitated in this case bythe fact that the LED has two facets on either side of its extendedwidth.

While not intended for imaging applications, this approach is aninexpensive way of improving the collection efficiency of the optic.

A lens array is provided for collecting light from a light source inwhich the light source emits divergent light. At least one lens isprovided having a compound shape including curved surfaces that arecentered about each side of the light source. The curved surface may bespherical or may have an offset aspheric shape. The lens may include aflat top portion separating the curved surfaces with the curved surfacesbeing equidistant from a center line extending through the light source.The lens includes geometry that is optimized for each portion of thelight source from which that section of the lens collects light.

The lens may include an approximated aspheric shape that includesfaceted surfaces that approximates an aspheric shape. The facetedsurfaces may be formed to have a symmetrically circular shape by a tool,such as, for example, a drill bit. Alternatively, the faceted surfacemay be formed of micro-pyramids forming a square tile pattern by a tool,such as, for example, a surface lathe or grinder.

These and other embodiments are described in more detail in thefollowing detailed descriptions and the figures.

The foregoing is not intended to be an exhaustive list of embodimentsand features of the present invention. Persons skilled in the art arecapable of appreciating other embodiments and features from thefollowing detailed description in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a typical point source light array with simpleplano-convex lenses having spherical surface profiles a point source oflight.

FIG. 2 is a view of a typical LED array emitting widely disparate lightwith simple plano-convex lenses.

FIG. 3 is a view of a single LED and associated lens in an array with aspherical lens having a compound shape. FIG. 3A is a view of a singleLED and the offset spherical lens having a compound shape.

FIG. 4 is a plot showing faceted surfaces approximating an asphericshape.

FIG. 5 is a partial cross-section of an LED array having a faceted lensin which the faceted surfaces are circularly symmetrical.

FIG. 6 is a top view of a lens array in which the faceted surfaces arein the form of micro-pyramids forming a square tile pattern.

DETAILED DESCRIPTION OF THE INVENTION

Representative embodiments of the present invention are shown in FIGS.3-7, wherein similar features share common reference numerals.

More specifically, FIG. 3 shows an LED 30 mounted on a circuit board 32with an associated lens 34 from an array that may comprise, for example,one thousand (1,000) LED's. Each LED 30 typically emits disparate lightfrom the sides 38 so that the light is widely dispersed. In order tomore effectively collect the light, lens 34 is formed of a compoundshape that includes a curved surfaces 40 separated by a flat surface 42.Curved surfaces 40 may have a spherical or offset aspheric shape 41, asshown in FIG. 3A, although in FIG. 3 a spherical surface is shown. Lens34 is centered about center line CL extending through LED 30 so thatlight from each side 38 of LED 30 is projected into the respectivecurved surface 40 on that side. Each curved surface 40 is centered abouta radius R extending from a center point 44. Each radius R extends fromcenter point 44 that lies directly above an imaginary light point sourceon each side of the LED 30. The location of center point 44 and lengthof radius R are determined by standard rules for finding a radius ofcurvature and center point distance for a piano-convex lens. Even thoughlight is emitted along the sides 38 of LED, center point 44 isdetermined by assuming a point source of fight at each side of LED 30.Thus, each side 38 of LED 30 emits light that primarily transmitsthrough what is effectively a piano-convex lens centered over that side38. The geometry of each spherical surface 40 is optimized for eachportion of the LED 30 from which it collects light. In other words, thedimensions of the lens 34 is determined by finding the preferredpiano-convex shape for collimating light on one side of the LED(assuming a point source of light) by standard rules known to thoseskilled in the art. However, each piano-convex shape (curved surface 40)is incorporated into a single lens separated by flat surface 42. Thisconfiguration effectively provides half of a lens on one side of the LED30 and another half of a lens on another side of the LED 30. FIG. 3A issimilar to FIG. 3 except that the spherical or aspheric shape has beenoffset 41 relative to the centerline of the LED axis.

Another aspect of this invention uses cut facets 46 to approximate theshape of a curved surface aspheric surface 48 as seen in FIG. 4. Curvedor aspheric surface 48 may be determined according to standard lensmakers formulas. For example, these formulas calculate the optimalaspheric shape for a collimating optic used with a highly divergentlight source, such as an LED. However, for the purposes of collectinglight from an LED in non-imaging applications, a precisely andexpansively manufactured aspheric lens surface is not needed. Light froman LED may be collected adequately by faceted surfaces 46 thatapproximate the aspheric surface 48.

As seen in FIG. 5, faceted surfaces 50 on lens 52 may be formed by atool or mold into which faceted surfaces 50 are machined by a tool thatworks like a drill bit, for example. For instance, the facet surfacesmay be formed on a drill bit, which is then used to form the mold. Theresulting lens may include faceted surfaces 50 that are circularlysymmetric as seen in FIG. 5. Faceted surfaces 50 are separated by a flatsurface 51. Lens 52 of FIG. 5 includes dimensions that are merelyillustrative and are not intended to be limiting.

Alternatively, as seen in FIG. 6, faceted surfaces 54 may be machined ina tool or mold for the lens 56 with, for example, a router or grinder.As seen in FIG. 6, the resulting lens 56 may include faceted surfaces 54that form micro-pyramids in a square tile pattern that fully fills thesurface of each lens 56. Faceted surfaces 54 are formed centrally alongperpendicular axes of symmetry. Each square lens 56, for example, mayhave equal sides having a dimension in the range of about 1 mm to about1.9 mm. In all the embodiments, the lens encapsulates the LED, which mayhave a width dimension of, for example, about 0.25 mm. Often tools formaterial removal might also apply, such as water-jet or laser cuttingtools.

As seen in FIGS. 5 and 6, the faceted surfaces can accommodate flattenedshapes necessitated in this case by the fact that the LED's 30, as seenmost clearly in FIG. 6, has faceted sides 58 on either side of itsextended width.

The lens array may be formed of a potting gel that is cured within atool or mold to have the desired configuration. The mold may be metalsuch as, for example, stainless steel. Alternatively, the lens array maybe formed of glass or other material that may be machined to the desiredconfiguration. Furthermore, the number of faceted surfaces may varyaccording to the desired precision. Additionally, the width of the lensin all embodiments may vary according to a number of factors such as,for example, the grid spacing of the LED's.

Persons skilled in the art will recognize that many modifications andvariations are possible in the details, materials, and arrangements ofthe parts and actions which have been described and illustrated in orderto explain the nature of this invention and that such modifications andvariations do not depart from the spirit and scope of the teachings andclaims contained therein.

1. A lens array, comprising: multiple lenses in a monolithic structure,for collecting light from an array of multiple LED light sources;wherein each LED light source emits divergent light, wherein for eachLED light source there is a lens having a first surface with a compoundshape of at least two curved portions separated by a flat portion thatis distributable around the LED light source and arranged to collimatethe light from the LED, wherein one of the curved portions is centeredabout a radius R extending from a first center point located directlyabove a first imaginary light point source positioned on a first lateralside of the LED and the other one of the curved portions is centeredabout a radius R extending from a second center point located directlyabove a second imaginary light point source positioned on a secondlateral side of the LED, and wherein each curved portion has a sphericalor an aspheric shape relative to its respective LED light source.
 2. Thelens array of claim 1, wherein the curved portions are equidistant fromthe center line of the LED light source and the flat portion isperpendicular to the center line.
 3. The lens array of claim 1, whereineach of the spherical or aspheric shapes are offset from a center lineextending through the each LED light source.
 4. The lens array of claim1, wherein each of the lenses is symmetric about a center line extendingthrough each LED light source.
 5. The lens array of claim 1, whereineach of the lenses includes sections that collect light from respectiveportions of each LED light source.
 6. The lens array of claim 5, whereineach lens section is optimized for each portion of each LED light sourcefrom which each section collects light.
 7. The lens array of claim 1,wherein each of the lenses includes an offset aspheric shape.
 8. Thelens array of claim 7, wherein each of the lenses has a faceted surfacethat approximates the offset aspheric shape.
 9. The lens array of claim8, wherein each of the faceted surfaces has a symmetrically circularshape.
 10. The lens array as in claim 1, wherein the curved portion isspherical.
 11. The lens array as in claim 1, wherein the curved portionis aspherical.
 12. The lens array as in claim 1, wherein the curvedportion is faceted.
 13. A method of manufacturing an LED light module,comprising: determining a configuration for an array of lenses so thatthere is a separate lens for each LED, wherein each lens has a firstsurface having a compound shape including at least two curved portionsseparated by a flat portion that is distributed around an LED arrangedto collimate the light from the LED, and the lens being disposed over anLED so that light from each side of the LED is projected into arespective curved surface; and one of the curved portions is centeredabout a radius R extending from a first center point that lies directlyabove a first imaginary light point source positioned on a first lateralone side of the LED and the other one of the curved portions is centeredabout a radius R extending from a second center point located directlyabove a second imaginary light point source positioned on a secondlateral side of the LED.
 14. The method of claim 13, wherein the lensarray is monolithically molded.
 15. The method of claim 13, wherein eachlens in the lens array is fabricated by machining faceted surfaces intothe lens array.
 16. The method of claim 15, wherein the shape of thelens array is formed by machining a mold using a drill bit-type tool.17. The method of claim 16, wherein each lens in the lens array ismachined using a circularly symmetric pattern.
 18. The method of claim15, wherein the shape of the lens array is formed by machining a moldusing a surface lathe, router, or grinder.
 19. The method of claim 14,wherein the lens array is formed by molding potting gel.
 20. The methodof claim 13, wherein the lens array is formed of glass.
 21. The methodof claim 20, wherein each lens in the lens array is circularlysymmetric.